The present invention relates to an electric machine                wherein the electric machine has a stator and a rotor,        wherein the rotor is movable relative to the stator in a direction of movement,        wherein when viewed in the direction of movement of the rotor, the stator is divided into stator segments adjoining one another,        wherein the stator segments each have a central region, a first transition region and a second transition region,        wherein when viewed in the direction of movement of the rotor, the central regions are arranged between the first transition region and the second transition region of the respective stator segment,        wherein the stator segments each have a stator yoke on the side facing away from the rotor which extends over the respective central region and the respective first transition region,        wherein starting from the stator yokes, central groove webs in the respective central region and first transition webs in the respective first transition region extend toward the rotor,        wherein on their side facing away from the rotor the stator segments each have a transverse web in the respective second transition region,        wherein starting from the respective transverse web, respective second transition webs extend toward the rotor in the respective second transition region,        wherein when viewed in the direction toward the rotor, the second transition webs end at the same height as the central groove webs,        wherein when viewed in the direction toward the rotor, lower edges of the stator yokes have a yoke spacing from the rotor.        
Electric machines have a stator which for its part has a stator yoke, starting from which webs extend toward the rotor. A stator groove is formed in each case between immediately adjacent webs. The stator winding system of the electric machine is arranged in the stator grooves.
In the simplest case, one winding half of a single winding of the stator winding system is arranged in each stator groove. The other half of the respective winding runs in another stator groove, in which case no winding half of another winding of the stator winding system is arranged in said groove. Such a stator winding system is normally referred to in the prior art as a single-layer winding.
Alternatively, it is possible that the winding halves of two windings of the stator winding system are arranged in each stator groove. The other winding half of the one winding and the other winding half of the other winding are arranged in two other stator grooves, in which case the first-mentioned stator groove is arranged between the two other stator grooves. Such a stator winding system is normally referred to in the prior art as a two-layer winding. Compared with a single-layer winding, a two-layer winding exhibits electromagnetic advantages and is therefore to be preferred as a rule.
Provided that the stator is a uniform part (viewed in the direction of movement of the rotor), it is easily possible to wind the stator with a two-layer winding. In the case of larger electric machines, both manufacturing advantages and also transportation advantages and also storage-related advantages are however offered if the stator consists of a plurality of segments (stator segments). In the case of such an embodiment of the stator a two-layer winding cannot readily be implemented.
It is known in the prior art to furnish the stator segments with a single-layer winding, for example a single-layer winding as is known from EP 2 166 644 A1. Although this solution can be readily implemented, the electromagnetic disadvantages which are associated with a single-layer winding are however accepted.
An electric machine of the type mentioned in the introduction is known for example from U.S. Pat. No. 7,772,738 B2. In the case of the electric machine from U.S. Pat. No. 7,772,738 B2 the transverse web constitutes a continuation of the stator yoke. The central groove webs, the first transition webs and the second transition webs are embodied the same. The stator segments adjoin one another edge to edge.
Although it is known from U.S. Pat. No. 7,772,738 B2 to arrange a two-layer winding in the grooves formed by the webs of the stator segments, in other words to furnish the stator segments with a two-layer winding, the two-layer winding from U.S. Pat. No. 7,772,738 B2 is however incomplete. In particular, while one of two winding halves of a first winding and one of two winding halves of a second winding are arranged in each case between two central groove webs, on the other hand only the second winding half of a first winding or the second winding half of a second winding is arranged in each case in the transition regions. The two-layer winding is therefore incomplete in the transition regions. An attempt is made in U.S. Pat. No. 7,772,738 B2 to compensate for the resulting disadvantageous electromagnetic effect in that the stator yoke and the transverse web exhibit a greater strength in the regions adjoining the adjacent stator segments than between said regions. The compensation is however only incomplete.
It is theoretically conceivable to complete the incomplete two-layer winding from U.S. Pat. No. 7,772,738 B2 at a later time. In this case, while the electromagnetic disadvantages would be resolved it is however difficult or almost impossible to ensure a high quality level of the subsequently produced windings. Rather, it must be expected that the operational reliability (dependability) of the electric machine is significantly reduced.